In drilling for oil and gas, drilling muds play an important role. Drilling muds are the fluids which are used to maintain pressure, cool drill bits, and lift cuttings from the drill holes. Although drilling muds vary in composition over a wide spectrum, generally, they fall into two classes; either aqueous formulations or oil formulations.
The choice of formulation used is dictated in part by the nature of the formation in which drilling is to take place. For example, in various types of shale formations, the use of conventional water-based muds can result in a deterioration and collapse of the formation. The use of an oil-based formulation circumvents this problem.
A conventional oil-based drilling mud formulation is comprised basically of the following ingredients: oil (generally a diesel oil), emulsifying agents (alkaline soaps of fatty acids), wetting agents (dodecylbenzene sulfonate), water (generally a NaCl or CaCl.sub.2 brine), barite, barium sulfate, or other weighting agents, and normally amine treated clays (employed as a viscosification agent).
More recently, neutralized sulfonated ionomers have been found to be particularly useful as viscosification agents in oil-based drilling muds. See, for example, U.S. Pat. No. 4,442,011 and U.S. Pat. No. 4,447,338.
These neutralized sulfonated ionomers are prepared by sulfonating an unsaturated polymer such as butyl rubber, EPDM terpolymer, partially hydrogenated polyisoprenes and polybutadienes. The sulfonated polymer is then neutralized with a base and thereafter steam stripped to remove the free carboxylic acid formed and to provide a neutralized sulfonated polymer crumb.
To incorporate the polymer crumb in an oil-based drilling mud, the crumb must be milled, typically with a small amount of clay as a grinding aid, to get it in a form that is combinable with the oil and to keep it as a noncaking friable powder. Often, the milled crumb is blended with lime to reduce the possibility of gelling when used in the oil. Subsequently, the ionomer containing powder is dissolved in the oil used in the drilling mud composition. Unfortunately, the crumb, either alone or with lime, is difficult to dissolve, which is an especially serious disadvantage in the field.
Accordingly, it is an object of the present invention to provide sulfonated polymers, including neutralized sulfonated polymers, in a form readily combinable with other drilling mud components.
Another object of the invention is to provide an improved method for preparing oil-based drilling mud compositions.
These and other objects w ill be readily appreciated upon a reading of the description which follows.